1. Field of the Invention
This invention relates to an exposure method and exposure system in the photolithography process, and in particular to a method and system using a plurality of exposure apparatuses to achieve precise photolithography.
2. Related Background Art
In recent years, reduction projection type exposure apparatuses have been used for the manufacture of super-LSI and have rendered great services in the improvement of productivity. Of the projection exposure apparatuses of the type, it is required to improve the superposition accuracy during the superposition exposure between different layers on semiconductor wafers, along with the tendency toward minuteness of the line width of the pattern on reticles to be projected and exposed and the tendency of the patterns themselves toward higher integration. This is particularly remarkable between different apparatuses. Recently, various projection exposure apparatuses different in numerical aperture, magnification or exposure area (projection field of view) have appeared and in super-LSI manufacturing factories, the exposure between different layers has often been used properly between discrete apparatuses in one process of manufacture of super LSI with the resolving power and throughput required being taken into account.
For example, there is known the so-called mix- and-matching manufacturing method in which, for example, proximity type exposure apparatuses or mirror projection aligners are used for the exposure of relatively large patterns and reduction projection type exposure apparatuses are used for the exposure of more minute patterns. In the case of this mix-and-matching, exposure apparatuses different in projection magnification and projection field of view or apparatuses different in exposure system like refracting systems or reflecting systems are used together and therefore, the matching accuracy becomes particularly important. As a factor which governs the matching accuracy, mention may be made of the distortion of projection optical systems. Generally, even in projection optical systems of the same structure, the distortion characteristic delicately differs at every system, and between projection optical systems different in magnification or field of view, the distortion characteristic may differ greatly. Accordingly, even if mix-and-match is effected by the use of such apparatuses, sufficient matching accuracy is not always obtained. This leads to a serious problem that productivity is reduced by unsatisfactory matching.
Further problems peculiar to the case of the mix-and-matching have been that the maintenance between entirely different apparatuses is cumbersome and that the presence of entirely different alignment marks on the masks and reticles necessary for the respective apparatuses makes the manufacture of the masks and reticles cumbersome and also leads to low efficiency of manufacture of semiconductive elements, which in turn has resulted in a bindrance to the enhancement of productivity.